Excitotoxicity is responsible for much of the neuron death caused by stroke, traumatic brain injury, and neurodegenerative disease. In excitotoxicity, high intracellular Ca2+ leads to cell death. Ca2+/calmodulin dependent protein kinase II (CaMKII) is a major mediator of physiological Ca2+ signaling and may participate in excitotoxicity, but it is not clear whether CaMKII is toxic or protective. It is clear that excitotoxic glutamate induces changes in CaMKII activity and localization. Glutamate increases CaMKII Ca2+/CaM- dependent activity, autonomous activity, translocation to synaptic sites, and extrasynaptic clustering. Excitotoxicity can also activate apoptosis, and some evidence suggests that CaMKII may influences apoptosis. The goal of this proposal is to investigate the role of CaMKII in excitotoxicity. Aim 1: Determine if CaMKII promotes excitotoxicity- Using pharmalogical CaMKII inhibitors, RNAi, and transfection, CaMKII activity and expression will be manipulated in primary dissociated hippocampal neurons. The effects of these manipulations on glutamate-induced excitotoxicity will be assessed. Aim 2: Determine which glutamate-induced change(s) in CaMKII activity and localization increase excitotoxicity- Endogenous CaMKII will be replaced with CaMKII mutants that mimic, enhance, reduce, or prevent one or more glutamate-induced change in CaMKII activity or localization. The affects of these mutants on glutamate-induced cell death will be measured. Aim 3: Determine the effects of CaMKII activity in apoptosis and/or necrosis in excitotoxicity- The ratio of apoptotic vs. necrotic cells following excitotoxicity with or without CaMKII inhibitor will be determined. Additionally, the affects of CaMKII inhibitor on components of the apoptosis pathway will be assessed. Significance: Stroke, traumatic brain injury (TBI), and neurodegenerative disease (ND) afflict millions each year, causing death or disability by damaging neuronal tissue through excitotoxicity. Knowledge of the pathways involved in excitotoxicity will provide additional targets for therapeutic interventions to prevent neuron death in stroke, TBI, and ND. This study investigates the role of one potential target for prevention of excitotoxicity, CaMKII.